Electronic plumb indicator for monopoles, survey poles, global positioning antennas and the like

ABSTRACT

Disclosed are electronic plumb indicators for monopoles, survey poles, global positioning antennas and the like. A exemplary plumb indicator comprises a substrate, a plumb bob suspended by a thread (e.g., wire, cable, string, etc.) and disposed over a first surface of the substrate, and a probe. The substrate has an array of conductive pads disposed over its first surface, preferably in a regular pattern. The probe has a first body portion held by the plumb bob but allowed to move freely in the vertical direction, and a conductive tip disposed between the plumb bob and the first surface of the substrate. The probe tip makes contact with the first surface of the substrate, and contacts one or more pads in normal operation. The pads may be scanned electronically to determine the location of the probe tip and plumb bob with respect to the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit priority under 35 U.S.C. §119(e) to U.S. patent application Ser. No. 60/199,078, filed Apr. 20,2000, the contents of which is incorporated herein.

FIELD OF THE INVENTION

[0002] The present invention relates to electronic plumb indicators formonopoles, survey poles, global positioning antennas and the like.

BACKGROUND OF THE INVENTION

[0003] There is a need in the surveying art and the global positioning(GPS) art to increase the speed and accuracy at which surveying polesand GPS antenna poles are plumbed to vertical positions.

SUMMARY OF THE INVENTION

[0004] Broadly stated, the present invention encompasses a plumbindicator comprising a substrate, a plumb bob suspended by a thread(e.g., wire, cable, string, etc.) and disposed over a first surface ofthe substrate, and a probe. The substrate has an array of conductivepads disposed over its first surface, preferably in a regular pattern.The probe has a first body portion in contact with a surface of theplumb bob, and a conductive tip disposed between the plumb bob and thefirst surface of the substrate. The probe tip makes contact with thefirst surface of the substrate, and contacts one or more pads in normaloperation. The pads may be scanned electronically to determine thelocation of the probe tip and plumb bob with respect to the substrate.

[0005] In preferred embodiments of the present invention, the plumb bobcomprises an elongated mass and cylindrical bore along a portion of thevertical center axis of the elongated dimension. Also in these preferredembodiments, the first body portion of the probe comprises a cylindricalshaft which is disposed within the cylindrical bore in the plumb bob,and the tip of the probe has a rounded or flat surface for contact withthe first surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 shows a first exemplary embodiment of a plumb indicatoraccording to the present invention.

[0007]FIG. 2 shows a cross-sectional view of the exemplary plumb bob andprobe shown in FIG. 1 according to the present invention.

[0008]FIG. 3 shows the first exemplary plumb indicator of FIG. 1 using asecond exemplary plumb bob and disposed within an exemplary pole housingaccording to the present invention.

[0009]FIG. 4 shows a cross-sectional view of a second exemplary plumbbob according to the present invention.

[0010]FIG. 5 is a top plan view of a portion of the top surface of asubstrate according to the present invention showing an exemplary layoutof contact pads according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011]FIG. 1 shows an exemplary plumb indicator 10 according to thepresent invention. Plumb indicator 10 comprises a substrate 20 which hasa first surface 21 and an array of conductive pads 24 disposed over thefirst surface 21. A plurality of mounting holes 26 are provided insubstrate 20 for mounting substrate 20 to a surveying pole or monopole,as described below in greater detail with reference to FIG. 3. Othermounting means may be employed in the present invention, and theparticular mounting means employed is not critical to the practice ofthe present invention.

[0012] Plumb indicator 10 further comprises a plumb bob 30 suspended bya thread 32 and disposed over first surface 21 of substrate 20, andfurther comprises a probe 40 held by plumb bob 30. The weight andpositioning of plumb bob 30, and the connection of thread 32 to a pointon the vertical center axis of bob 30, enable the vertical center axisof bob 30 to be substantially perpendicular to substrate 20 whenindicator 10 is placed in a plumb position. In a preferred embodiment,as shown in the cross-sectional view of FIG. 2, probe 40 has a bodyportion 42 which fits within a cylindrical bore 34 made at the bottom ofplumb bob 30 and along the vertical center axis of plumb bob 30, and aconductive tip 44 disposed at the lowermost distal end of body portion42. Body portion 42 and bore 34 both preferably have circularcross-sections. Body portion 42 freely moves in the vertical directionwithin bore 34, and portions of the outer surface of body portion 42contact with respective portions of the inner surface of bore 34 to keepbody portion 42 and probe 40 aligned substantially parallel with thevertical center line of plumb bob 30. This in turn places the probe 40in a position which is perpendicular to substrate 20 when indicator 10is placed in the plumb position with respect to the earth (due togravity, plumb bob 30 seeks a stationary state where its vertical centeraxis is perpendicular to the surface of the earth).

[0013] Probe tip 44 can have a flat surface with beveled edges, or arounded surface (e.g., spherical, hemispherical, or semi-hemispherical)for contact with surface 21 of substrate 20 and the pads 24 thereon. Inthe former case, there preferably is a sufficient gap between thesidewalls of probe body 42 and bore 34 to allow probe tip 44 to remainflat through the arc motion of plumb bob 30. Probe tip 44 may have aconductive rubber coating on its surface to minimize scratching of theconductive pads 24 while plumb bob 30 freely moves around abovesubstrate 20 during the plumbing process. Probe 40 touches pads 24 onaccord of its own weight, and does not require a spring behind it. Theposition of plumb bob 30 relative to substrate 20 is found bydetermining which pads 24 are being contacted by probe tip 44. As oneexample, a voltage (or ground) may be applied to metal bob 30 throughthread 32 and coupled to a metal probe 40 by surface contact with bore34, and the pads 24 may be scanned electronically to detect which pad orpads have the same potential as bob 30. A detector 50, which preferablycomprises a microprocessor unit, may be used for the scanning anddetection, and digital multiplexers may be used to selectively group thepads for scanning. As another way, the pads 24 may electrically coupledin a row-column format so that probe tip 42 electrically couples atleast one row with at least one column. The rows and columns may bescanned by detector 50 to determine which rows are being coupled towhich columns by tip 42. In this case, there is no need to couple anelectrical potential to thread 32, although such can be done. Thisembodiment is described in greater detail below with respect to FIG. 5.To achieve a 1 mm accuracy in finding the position of probe 40 on firstsurface 21, the pads may be set to square dimensions of 0.2 mm on a sideand spaced apart from one another by gaps of 0.2 mm, and the probe tip44 may be formed to provide a contact area to surface 21 of 0.5 mm.

[0014] In one embodiment according to the present invention, plumb bob30 comprises a cylinder of heavy material with a diameter of 10 mm, aheight of 100 mm, a center bore 34 of 1 mm to accommodate free verticalmotion of a 0.6 mm diameter probe 40. The top end of thread 32 andsubstrate 20 may each be fixed to a housing or other support means ofany desired type, and substrate 20 and/or the top end of thread 32 maybe aligned so that probe tip 44 comes to rest on a particular set of oneor more pads when plumb bob 30 is in the plumb (vertical) position withrespect to the earth.

[0015] Referring to FIG. 3, plumb indicator 10 can be housed inside apole, such as a surveying pole or a monopole used to position a GPSantenna (in the latter case, the GPS antenna is mounted to the top ofthe monopole). Substrate 20 is affixed to a widened portion of the polewith mounting screws that pass through the mounting holes 26. The top ofthread 32 may be fixed to the pole by a plug assembly disposed withinthe tube near the top end and secured thereto by screws, glue, or otherattachment means. The plug assembly preferably centers thread 32 withinthe tubing of the pole at the top of the pole. Mounting holes 26 mayhave sufficient diameter with respect to the securing screws to enable acontrolled amount of lateral movement of substrate 20 with respect tothe vertical axis of the pole. With this lateral movement, substrate 20may be aligned so that probe tip 44 contacts a desired set of pads 24when plumb bob is placed in the plumb position.

[0016] As shown in FIG. 4, plumb bob can also have side bars to protectit against falling down into the inside of the pole, if the pole is heldupside down. An annular plate may also be used for this purpose. Thepole may have a typical diameter of 30 mm and plumb bob 30 may have atypical diameter of 10 mm, in which case the motion of the plumb bob andthe probe 40 is contained within a circle having a diameter of 20 mm (30mm diameter of the pole minus 10 mm diameter of the plumb bob).

[0017]FIG. 5 shows a top plan view of a preferred embodiment for layingout contact pads 24. A partial array of six rows R1-R6 and six columnsC1-C6 is shown. The pads 24 are arranged in a checker-board red/blackarrangement: row pads being assigned to red blocks, and column padsbeing assigned to black blocks. All of the pads of each row areelectrically connected together and routed to an input/output port ofdetector 50, and all of the pads of each column are electricallyconnected together and routed to a input/output port of detector 50. Theconnection and routing may be readily accomplished by using amulti-layer printed circuit board where the pads are formed on the topmetal layer, where another wiring layer of the board is used to couplethe pads of respective rows together with a plurality of metal tracesand a plurality of vias to the row pads, and yet another wiring layer isused to couple the pads of respective columns together with a pluralityof metal traces and vias to the column pads. These metal traces in theunderlying metal layers are shown by dashed lines in FIG. 5. Using asquare pad area of 0.2 mm on a side, and a spacing distance of 0.2 mmbetween pads, 50 rows and 50 columns can cover a 20 mm by 20 mm squarearea. The surface area covered on substrate 20 by probe tip 44 is shownby a broad dashed circle in FIG. 5. In one implementation, a voltage(such as either supply VDD or ground) is applied to probe tip 44, andeach row and column is wired to another voltage (such as either groundor supply VDD) through a respective resistor. The probe tip will bringthe columns and rows which it overlies to its potential, and thispotential can be detected by scanning all the rows and columns andlooking for a digital logic level that corresponds to the voltage of theprobe tip 44.

[0018] As another implementation, no voltage is applied to probe tip.Each row is coupled to one of the digital logic potentials (such aseither ground or VDD) through a respective resistor. Detector 50 thenselectively applies the opposite digital logic voltage, referred toherein as the “test voltage,” to each column while scanning all the rowsto determine if a row has the voltage of the selected column. To speedthis process, a binary-tree scan search may be done. For example, thetest voltage may be first applied to column 1-25 to see if there is amatch, and then to columns 26-50 if no such match is found. If amatching row is found when the test voltage is applied to columns 1-25(or alternatively to columns 26-50), then the search is narrowed byapplying the test voltage to columns 1-12 (or alternatively to columns26-37), and then to columns 13-25 (alternatively 38-50) if no match isfound in columns 1-12 (alternatively 26-37). This process is continueduntil a small set of rows and columns are reached, at which point thetest voltage can be individually applied to the columns of the smallset. Of course, an equivalent implement of the above may be made byinterchanging the function of the rows and columns. As a modification,multiplexed row and columns buffers may be used to connect the rows andcolumns to detector 50, which may be a microprocessor. The aboveapproach may find that tip 44 covers two rows at a time, and/or twocolumns at a time. If so, the position may be computed as being betweenthe adjacent rows and columns (i.e., average the positions of theaffected rows and columns).

[0019] Detector 50 does not need to wait for plumb bob 30 to bestationary. It may scan the entire pads at least 50 times per second anddetermines the center of the motion. The period of the motion of plumbbob 30 (which is a pendulum) is 2*Pi*SQRT(L/g), where L is the length ofthe thread and g is the gravity constant. For a one meter length L, theperiod is about 2 seconds. Detector 50 can read at least one pendulumcycle of data (at least 100 snapshots) with a period, and from thisdetermine the center of the pendulum swing relative to the center of thearray of pads 24.

[0020] Detector 50 can show the results by a LED display or by sendingthem via serial port (RS-232 connection or other types of connectionports to a handheld device that shows the location of the plumb bobgraphically. The operator may use the information to plumb the pole, orthe computer can take the offset into account to determine the locationof the survey point. In the latter case the pole must be orientedaccording a convention known to the handheld device.

[0021] It may be appreciated that pads 24 may be arranged in a radialpattern, with a the rows being concentric circles disposed around thecenter point of substrate 20, and the columns being disposed radiallyform the center point. In this implementation, the probe tip 44 residesat the center point when plumb bob 30 is in the vertical plumb position.It may also be appreciated that larger pads may be used at the outeredges of the array, such as by replacing a 2-by-2 grouping of pad by asingle pad that occupies the same area.

[0022] While the present invention has been particularly described withrespect to the illustrated embodiments, it will be appreciated thatvarious alterations, modifications and adaptations may be made based onthe present disclosure, and are intended to be within the scope of thepresent invention. While the invention has been described in connectionwith what is presently considered to be the most practical and preferredembodiments, it is to be understood that the present invention is notlimited to the disclosed embodiments but, on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the scope of the appended claims.

What is claimed is:
 1. A plumb indicator comprising: a substratecomprising a first surface and an array of conductive pads disposed overthe first surface; a plumb bob suspended by a thread and disposed overthe first surface of the substrate, said plumb bob having a firstsurface; and a probe having first body portion having portions thereofin contact with portions of the first surface of the plumb bob, andfurther having a conductive tip disposed between the plumb bob and thefirst surface of the substrate and in contact with the first surface ofthe substrate.
 2. The indicator of claim 1 wherein the probe does notrestrict the motion of the plumb bob.
 3. The indicator of claim 1wherein the pads are disposed in a matrix pattern on the first surfaceof the substrate.
 4. The indicator of claim 1 further comprising adetector coupled to the array of pads for sensing one or more conductivepads which are in contact with the probe's conductive tip.
 5. Theindicator of claim 1 wherein the pads are disposed in a matrix patternof rows and columns, where every other pad in a row is electricallyconnected together, and wherein every other pad in a column iselectrically connected together.
 6. The indicator of claim 5 furthercomprising a detector coupled to the array of pads which selectivelyapplies a test voltage to the columns of the pad array and scans therows for voltages which match the test voltage.
 7. The indicator ofclaim 5 further comprising a detector coupled to the array of pads whichselectively applies a test voltage to the rows of the pad array andscans the columns for voltages which match the test voltage.
 8. Theindicator of claim 5 further comprising a test voltage applied to theprobe tip, and a detector coupled to the array of pads which scans therows and columns for voltages which match the test voltage.